Typically, a shadowless lamp for preventing a shadow from being cast over a surgical field is placed, as a lighting system illuminating the surgical field, in an operating room (see, e.g., PATENT DOCUMENT 1). The shadowless lamp includes a lamp unit including many lamps, and the lamp unit is usually attached to the ceiling of an operating room through a movable mechanism. The shadowless lamp is used while the location of the lamp unit is adjusted as required by a doctor actually performing a procedure.